Aleutian disease (AD) in mink and ferrets will be used to determine functional relationships between antibody avidity and virus structure as a basis for chronicity patterns and development of proliferative lesions associated with immune complexes. Procedures based on virus isolation with immunoadsorbents will serve as a basis for determining antibody avidity, and procedures utilizing competitive binding of immunoglobulins taken during the course of AD on infected fixed-feline kidney cells (or mink kidney cells) will provide numerical values for binding avidities (by labeling each with 125I or 131I). Immune complexes will be quantitated by competitive inhibition of uptake of 125I-labeled heat-aggregated mink IgG on peritoneal macrophages and isolated by centrifugation on sucrose gradients from sera obtained during the course of AD, labeled with 125I, and classified according to densities and sedimentation coefficients. It is intended that these studies will provide information on: 1. The functional relationships between antibody affinity and virus structure as a basis for chronicity patterns of certain viral/immune complex diseases; 2. The association constants of subpopulations of anti-ADV in the course of AD; 3. Quantification of immune complexes in the course of AD; 4. The development of vasculitis in AD as a function of deposition of immune complexes.